In order to successfully raise and breed aquarium fish such as goldfish, fresh water tropical fish and marine fish it is necessary to use a filter devise capable of purifying the aquarium water by trapping and breaking down debris such as fish waste and excess fish food.
A cross section diagram FIG. 6 is an example of a conventional filtering device, commonly called the open system. Medium such as glass wool (21) and ceramic beads (22) are layered to form a filtration layer. Water in the tank (23) is siphoned by a pump (24) then passing through multiple holes (not shown) in the sprinkler head (25) and sprayed over the filtration layer. First the larger debris is trapped by the glass wool (21), next the ceramic beads (22) function as biological filter (bacteria in the medium breaks down the organic material such as fish waste, decomposing plants matte, fish food, etc. into nitrate, a harmless compound). Then the filtered water is returned to the tank (23).
System such as the ones described above is either fixed at the upper part of a tank as part of the cover or placed separately from the tank. There are several drawbacks to this type of filtration device. To accommodate larger quantity of filter medium, larger aquarium requires a larger filtration device relative to the aquarium capacity. Larger filtration device takes away from the esthetic value of an aquarium. In a larger device when the filter medium is not completely even in consistency water in the filtration device tends to follow its own narrow path instead of filtering throughout the medium, whereby causing an uneconomical and inefficiency condition called channeling. Increasing the speed of water flow through the system can make a smaller sized filtration device to function sufficiently, but the turbulence from fast flowing water may affect the fish adversely.
In order to promote the growth of necessary bacteria, the open system is designed to expose the filter surface for oxygen intake, but this allows the necessary element for plant growth, carbon dioxide, to escape and retards the growth of aquarium plants.
Further more, to keep the aquarium water consistently clean; filter medium must be cleansed or replaced regularly. In the conventional filtering device, removing and replacing specific filter medium could not be performed readily. As a result sudden and unexpected drop in the number of beneficial bacteria occurs from removal of the entire filter medium for cleaning and replacement FIG. 7, a schematic cross section diagram, illustrates another type of conventional filtration device commonly known as the sealed system. In this system, water from the tank (23) is siphoned up by a pump (24) and forced through a sealed cylinder or column (26) containing layers of several different types of filter medium (27). Similar to the aforementioned system, water will establish its own narrow path in the areas of least resistance in the filter medium (27) resulting in channeling where only a very limited portion of the filter medium is actually utilized. Difficulty in changing or cleaning the filter medium as well as the placement requirement of the device at a level below the tank (23) to insure the release of gas developing in the system are other disadvantages.